Such a spar cap assembly is disclosed by United States patent application publication 2013/0049249. The prefabricated spar cap assembly is integrated into a rotor blade half-shell after the curing of a polymer matrix in which the carbon fibers are embedded.
Since the carbon fibers forming the spar cap are electrically conductive, special measures for effective lightning protection are required in the case of such a rotor blade. These include, in particular, effective potential equalization between a lightning conductor, which is incorporated in the wind turbine rotor blade and connects a lightning receptor arranged particularly at the tip of the blade to the root of the blade, and the spar cap. The potential equalization can have the effect of preventing an electromagnetically induced discharge of a high lightning-stroke current by way of the lightning conductor from causing such great differences in potential between the lightning conductor and the spar cap that voltage flashovers occur. As a result, damage to the wind turbine rotor blade by a lightning strike can be avoided.
U.S. Pat. No. 7,494,324 discloses a wind turbine rotor blade in which an internal, electrically conductive spar is connected to an adjacently arranged lightning conductor. Provided for this purpose are potential-equalizing elements, which connect the spar and the lightning conductor to one another by way of an electrical line. The contact with the spar is established by way of a conductive ribbon.
U.S. Pat. No. 6,457,943 discloses a wind turbine rotor blade with a number of electrically conductive spar caps of a carbon fiber material. To increase the electrical conductivity of the spar caps, metal-coated carbon fibers are used, so that the current-carrying capacity of the spar caps should be sufficient for use as a lightning conductor. In addition, a centrally arranged metallic lightning conductor may be used. The spar caps and possibly the additional metallic lightning conductor are connected to one another at a number of longitudinal positions by way of potential-equalizing elements in the form of internal electrical conductors.
U.S. Pat. No. 7,651,320 discloses a wind turbine rotor blade with electrically conductive main spar caps of a carbon fiber material and two lightning conductors arranged inside the rotor blade. Potential equalization between a main spar cap and a lightning conductor is established by way of a copper mesh, which electrically contacts the main spar cap, and an electrical connecting line. A middle portion of the connecting line is screwed to the lightning conductor. A free end of the connecting line is screwed along with metallic adapters and the copper mesh to a lightning receptor.
U.S. Pat. Nos. 8,896,980 and 8,191,255 disclose a wind turbine rotor blade in which a flat or braided lightning conductor is arranged in the region of a web. The lightning conductor is integrated into a laminate in a vacuum-infusion process during the production of the wind turbine rotor blade.